Stringed instruments may be divided generally into two catagories -- bowed and plucked. The violin is an example of a stringed instrument in which the vibrations of the strings to produce musical sounds are initiated by rubbing the strings with a bow. The guitar is an example of a stringed instrument in which the vibrations of the strings to produce musical sounds are initiated by plucking the strings with the fingers or with a plectrum. In each of the examples given the strings of the instrument are stretched tightly along the body and neck with varying tensile forces of great magnitude. The neck structure in particular is subjected to forces tending to warp and twist it from its original shape.
The musical notes produced by stringed instruments in which the strings are stretched along the neck member are varied by pressing the strings against the neck with the fingers to change the length of the vibrating strings. In order to play the instrument with reasonable facility the strings must be accurately spaced from the neck in uniform fashion. Any twisting or warping of the neck member disrupts this uniformity of spacing and usually results in difficulty in holding the strings properly against the neck, or, in the case of a fretted neck, an undesirable buzzing sound produced by the strings vibrating against the frets. The undesirable twisting or warping may result from the tensile force produced by the stretched strings alone, or, in the case of wooden instruments, changes in temperature and humidity may contribute to the distortion.
The problem of providing reinforcement for the necks of stringed instruments is not new and has been met with varying degrees of success. It has been proposed in the past to employ a steel shaft as a truss rod within a wooden neck. In U.S. Pat. No. 1,652,627 to Jerome it was proposed to make the entire frame of the instrument in a unitary casting of metal, preferably aluminum, possessing rigidity, strength, resonance and lightness. In U.S. Pat. No. 3,915,049 to Bean it was proposed to make the neck of the instrument of extruded aluminum with at least one groove running the length thereof to improve the efficiency of sound transfer to the soundboard. The use of exposed metal surfaces on portions of the neck which are touched by the hand or fingers of the player is not desirable. If the metal is aluminum a black oxide will be formed and will rub off on the hand of the player. Furthermore, a player accustomed to the warm feel of wood will not readily accept a metallic substitute.